The 34-year-old and husband Freddie Prinze Jr became parents for the first time when she gave birth to their daughter Charlotte Grace.
Asked how she keeps in shape, she said to Access Hollywood: 'I just chase my toddler. That pretty much keeps [me] on my toes and puts me to bed by 8:30!'
The former Buffy star will return to screens later this year in new drama Ringer and said she's looking forward to her show.
She said: 'It's really the right channel. One of the things I loved so much about being on Buffy on the WB was you had this really familiar experience.
'It wasn't corporate - you could talk to all of the bosses. It was very open. The cast was always so friendly. Having been here for about 35 seconds, everybody is so nice!'